This invention relates to microwave circuits and, more particularly, to a coupler of electromagnetic energy in a microwave circuit employing coaxial lines of square conducting elements.
Cross-reference is hereby made to three copending applications pertaining to microwave systems assigned to the same assignee; "Coaxial Transmission Line Crossing" invented by T. Hudspeth and H. H. Keeling, Ser. No. 468,827, filed on 23 Feb. 1983; "Ferrite Modulator Assembly For Beacon Tracking System" invented by T. Hudspeth, H. S. Rosen and F. Steinberg, Ser. No. 469,870, filed on 25 Feb. 1983; and "Coaxial Line To Waveguide Adapter" invented by T. Hudspeth and H. H. Keeling, Ser. No. 468,825, filed on 23 Feb. 1983. These applications are hereby incorporated by reference in their entirety.
An important use of microwave circuitry is found in the construction of satellites which orbit the earth to serve as communication links among various stations on the surface of the earth. Such microwave circuits are utilized to receive and retransmit signals between the satellite and the earth station. The microwave circuitry is also utilized in the development of tracking signals for orienting the satellite and for directing the antennas in the requisite direction for communication with the stations. In one form of tracking mode, a beacon signal on the earth is sent to the satellite. The satellite receives the beacon signal by an antenna and a signal processing circuit develops azimuth and elevation error signals by which the satellite is able to correct its orientation. The arithmetic manipulations of the sum channel, the azimuth channel and the elevation channel in producing the orientation error signals are also accomplished by microwave circuitry.
In the construction of a satellite, it is important to construct the microwave circuits with a physical structure that insures their long-term reliability. It is also important to construct the circuits in a fashion that can withstand the forces of liftoff, vibrations, and other sources of physical stress which may be present in a satellite.
A form of construction which has enjoyed much success is the construction of microwave circuits within a solid plate of electrically conducting materials, preferably a light weight metal such as aluminum. The microwave structures are formed, in part, by milling out channels in the surface of the metallic plate for the conduction of electromagnetic signals in a range of, for example, 4-6 GHz (Gigahertz) as well as other bands. A cover plate is then placed on top of the base plate with the milled channels to close off these channels to form the passageways for the propagation of the electromagnetic energy.
One form of physical structure for the electromagnetic passages is the coaxial line formed of an outer conductor of square cross-section, and having an inner conductor, also of square cross-section. Both the inner and outer conductor are formed of metal. This type of structure is advantageous in satellites due to the wide bandwidth, compact size, low propagation loss, and adaptability for distribution networks and for multiple element antenna feeds.
A problem arises in the use of the foregoing square coaxial line in that the components thereof must be carefully fitted in place to insure proper transmission of electromagnetic energy. The components must also be rigidly secured to insure that they do not move from their designated places under the stresses to which a satellite may be subjected. In the past, these mounting requirements have been met by the use of specially fabricated support structures which required more time than is desirable for the insertion and positioning of the support structures within the microwave circuit. In addition, the physical structure did not provide for as good an impedance match or for the coupling of electromagnetic energy over the same spectral band as might be desired.